1. Field of the Invention
This invention generally relates to a method of forming an optoelectronic conversion layer. More particularly, the present invention relates to a method including a process of stacking a metal precursor layer with a nonmetal precursor layer and a thermal treatment to have the metal precursor layer react with the nonmetal precursor layer and thereby obtain an optoelectronic conversion layer.
2. Description of the Prior Art
Optoelectronic conversion layers, which can absorb light of specific frequency and convert it into electric energy, are widely used as light absorption layers in solar cells or photosensitive layers in photosensors.
Usually, materials used in current optoelectronic conversion layers may comprise copper-indium-gallium-selenide alloys, which can be mainly fabricated by two methods: one by co-evaporation and the other one by sputtering, combined with a selenization step. Both methods, however, have their own drawbacks. The co-evaporation method, for example, is only suitable for small-scale devices. When the co-evaporation is applied in a fabrication of large-level devices, CIGS alloys formed by this method may have poor distribution uniformity and therefore produce relatively low optoelectronic conversion efficiency. On the other hand, in the sputtering combined with selenization, the amount of gallium elements away from a substrate (or nearby a surface of the CIGS alloy) is relatively low, and the amount of gallium elements near the substrate (or away from the surface of the CIGS alloy) is relatively high because of a segregation of the gallium elements. Because of these drawbacks, an energy bandgap near a PN-junction would be relatively low and an open-circuit voltage (Vos) would also be reduced. Additionally, selenization is deemed as a non eco-friendly method, for it has to use toxic gases, i.e. hydrogen selenide (H2Se).